1. Field of the Invention
The present invention relates generally to a blanket-to-blanket type (hereafter BB-type) printing press. More specifically, the invention relates to a BB-type printing press with a divided plate cylinder, having independently adjustable rotational phases of the divided plate cylinder components.
2. Description of the Related Art
The BB-type printing press generally comprises a pair of blanket cylinders respectively coupled with plate cylinders. The blanket cylinders are arranged in juxtaposition for movement toward and aft from each other. The pair of blanket cylinders defines there between a path for feeding a web paper to pass therethrough. While the web paper travels through the path defined by the pair of blanket cylinders, printing is performed on both sides of the web paper.
On the other hand, it is known in the prior art to employ a divided plate cylinder for the BB-type printing press. The divided plate cylinder includes two plate cylinder components separated from each other in an axial direction. These plate cylinder components independently adjusted for relative angular phase therebetween.
A rotation in an associated rotating condition means the following phenomenon caused on the periphery of a driven side cylinder when the plate cylinder carrying one or more printing plates thereon and the blanket cylinder mounting a blanket on the periphery thereof are arranged in side-by-side juxtaposed relationship and driven by a gear train with the identical pitch circle diameters and identical number of gear teeth for rotation at the same speed in the opposite direction, and when the finishing diameter of the cylinder at the driving side is set greater than that of the driven side. Namely, with the contact pressure exerted by the periphery of the cylinder at the driving side, the peripheral speed of the driven side cylinder tends to rotate at the same rotation speed to the driving side cylinder. In other words, the rotational phase of the driven side cylinder is offset following to the rotational phase of the driving side cylinder within a tolerance range of phase shift due to backlash in the gear train, in the range of which the driving force transmitted through the gear train is not effective and thus cannot be externally controlled. In such condition, since the driven side cylinder is caused free angular displacement relative to the driving side cylinder, the contact phase of the cylinders may fluctuate depending upon temporary variation of contact pressure on the contacting peripheries of the cylinders. This makes is uncertain to establish desired phase relationship between the driving side cylinder and the driven side cylinder and rather permits offset within the angular range of the backlash of the gear train.
On the other hand, for high quality and clear printing, it is essential to establish precisely constant position of transferring printing pattern from the printing plate or plates on the plate cylinder to the blanket cylinder. The rotation in an associated rotating condition caused between the plate cylinder and the blanket cylinder may not be synchronized in rotational phases of the plate cylinder and the blanket cylinder to cause register error to degrade quality of printing pattern. Typically, fluctuation of the relative rotational phase between the plate cylinder and the blanket cylinder is reflected by lowering of sharpness of the printed pattern and by doubling of the printed pattern in the worst case.
Slightly differentiating the finishing diameter of the plate cylinder, on which the printing plate or plates are mounted and the finishing diameter of the blanket cylinder, on which the blanket is mounted, has been known in an equal diameter cylinder arrangement, a true-rolling cylinder arrangement and so forth.
Japanese Unexamined Patent Publication (Kokai) 61-182951 proposes a technology for preventing rotation in the associated rotating condition in BB-type printing press employing a normal, integral plate cylinder. Although the shown technology may be effective for prevention of the rotation in the associated rotating condition as long as the plate cylinder is not separated into two components, a difficulty i encountered in prevention of the rotation in the associated rotating condition in case of the divided plate cylinder. For facilitating understanding of the present invention, brief discussion will be given herebelow about the difficulty in prevention of the rotation in the associated rotating condition caused in the prior art with reference to FIG. 5.
FIG. 5 shows a plan view of the BB-type printing press in the prior art, which employs a driving means. The shown example is directed to the BB-type printing press construction, in which a pair of divided plate cylinders 1 and 1' are employed. Respective of the divided plate cylinder 1 and 1' includes main body side plate cylinder 1a and 1a' and divided cylindrical plate cylinder 1b and 1b". A pair of blanket cylinders 2 and 2' are arranged in juxtaposition to respectively associated divided plate cylinders 1 and 1' and to each other. The blanket cylinders 2 and 2' are supported on a drive side frame 3 and an operation side frame 4 in movable fashion for movement toward and aft from each other. The pair of blanket cylinders 2 and 2' are provided with finished diameters slightly greater than the finished diameters of the pair of divided plate cylinders 1 and 1' (1a and 1b, and 1a" and 1b").
In the construction of FIG. 5, the drive means is constructed as follow. At first, an intermediate gear 5 connected to a driving power source is engaged to a transfer gear 6 mounted on the end of a shaft of the main body side plate cylinder 1a. The transfer gear 6 is meshed with a transfer gear 7 mounted on the end of a shaft of the blanket cylinder 2. Through the gear train set forth above, the driving torque from the driving power source is transmitted to the transfer gears 6 and 7 for driving the main body side plate cylinder 1a and the blanket cylinder 2 in mutually opposite directions. With the shown path of driving torque transmission, since the main body side plate cylinder 1a having smaller diameter is positioned upstream side of the blanket cylinder 2 which has the greater diameter, no rotation in the associated rotating condition can be caused.
Then, the transfer gear 7 mounted on the end of the shaft of the blanket cylinder 2 is meshed with an intermediate gear 8 which is rotatably supported on the end of a shaft of the blanket cylinder 2' for free rotation relative thereto. The intermediate gear 8 meshes with a transfer gear 9 mounted on the end of a shaft of the main body side plate cylinder 1a' on the opposite side. The transfer gear 9 meshes with a driven gear 10 which is mounted on the end of a cylinder shaft of the blanket cylinder 2'. Therefore, the main body side plate cylinder 1a' and the blanket cylinder 2' are also driven to rotate in mutually opposite directions in synchronism with rotation of the main body side plate cylinder 1a and the blanket cylinder 2. Similarly to the above, in the power transmission path set forth above, since the main body side plate cylinder 1a" having the smaller diameter is the greater diameter. Therefore, no rotation in the associated rotating condition can be occurred.
On the other hand, driven gears 12 and 14 of the divided body side plate cylinders 1b and 1b' are engaged to transfer gears 11 and 13 respectively mounted on the opposite ends of the shafts of the blanket cylinders 2 and 2'. The transfer gears 11 and 13 are driven to rotate together with the blanket cylinders 2 and 2' when the latter are driven by the driving torque transmitted through the drive side gear train as set forth above. The rotational torque on the transfer gears 11 and 13 is thus transmitted to the driven gears 12 and 14 to rotatingly drive the divided body side plate cylinders 1b and 1b'. As can be appreciated, in the shown driving power transmission path at the operation side, the blanket cylinders 2 and 2' having greater diameters are located upstream side of the divided body side plate cylinders 1b and 1b' having smaller diameter. Therefore, rotation in the associated rotating condition may be caused on the divided body side plate cylinders 1b and 1b' to lower sharpness of the printed pattern and to cause doubling of the printed pattern in the worst case.